1. FIELD OF THE INVENTION
The present invention relates to a hydraulic brake apparatus for a vehicle, and more particularly to the apparatus having an auxiliary pressure source for generating a power pressure and a valve assembly for regulating the power pressure into a regulated pressure.
2. DESCRIPTION OF THE RELATED ARTS
As for the hydraulic brake apparatus having the auxiliary pressure source and the valve assembly, the U.S. Pat. No. 4,986,613 (corresponding to Japanese Patent Laid-open Publication No.2-41965) discloses a hydraulic braking system having an auxiliary cylinder which increases a hydraulic brake pressure from a master cylinder without causing any excessive braking force applied to wheel brake cylinders. In this system, the auxiliary cylinder is adapted to increase a hydraulic brake pressure applied to the wheel brake cylinders, when one of a hydraulic power pressure generated by the power source and a hydraulic pressure generated by a hydraulic booster is less than the hydraulic brake pressure by a predetermined difference. The auxiliary cylinder is allowed to be in its operative condition only when one of the hydraulic pressures generated by the power source, the hydraulic booster and the master cylinder is less than a predetermined value.
According to the above hydraulic braking system, the auxiliary cylinder is arranged in parallel with, but separated from the master cylinder and the hydraulic booster which are combined to be integral. Therefore, the system as a whole will be large in scale, and piping of hydraulic pressure circuits will be complicated to cause a difficulty in designing the system, which will be a great bar when minimizing the system, and which will raise its manufacturing cost.